1. Field of the Invention
This invention relates to a method for displaying autoradiograph.
2. Description of the Prior Art
Autoradiography has been known as a method for obtaining information on location of radioactively labeled substances which are distributed in at least one-dimensional direction to form rows consisting of plural bands on a support medium.
For instance, the autoradiography comprises steps of: labeling organism-originating biopolymers such as proteins or nucleic acids with a radioactive element; resolving (developing) the radioactively labeled biopolymers, derivatives thereof, cleavage products thereof or synthetic products thereof on a support medium through a resolving process such as gel electrophoresis; placing the support medium and a high-speed X-ray film together in layers for a certain period of time to expose the film; developing said film; obtaining information on location of the radioactively labeled substances from the developed film; and then performing the identification of the polymeric substances, determination of molecular weight thereof or isolation thereof based on the obtained locational information.
Recently, the autoradiography has been effectively used especially for determining the base sequence of nucleic acid such as DNA or RNA. Further, the autoradiography has been used as an essential means in the screening of gene wherein a hybridization method such as southern blotting, northern blotting or western blotting is employed.
Japanese Patent Provisional Publications No. 59 (1984)-83057 and No. 60(1985)-10174 and Japanese Patent Application No. 58(1983)-173393 (which correspond to U.S. applications Ser. No. 837,037, now pending as Ser. No. 07/378,509; No. 624,813 now pending under Ser. No. 07/127,605; and No. 651,279 now pending under Ser. No. 07/431,701, respectively) disclose a radiation image recording and reproducing method using a stimulable phosphor sheet in place of a conventional radiography using a radiosensitive material such as an X-ray film. Said method comprises causing a stimulable phosphor in the stimulable phosphor sheet to absorb radiation energy and exciting the stimulable phosphor with an electromagnetic wave (stimulating rays) such as visible light or infrared rays to release the radiation energy from the phosphor sheet as light emission. This method enables exposure time to be greatly shortened and does not suffer chemical fog which is a problem associated with the conventional radiography. Further, this method has an advantage in that the autoradiograph having locational information on the radioactively labeled substances can be obtained in the form of symbols and/or numerals in addition to a visible image, because the autoradiograph can be stored in the phosphor sheet as the radiation energy and read out as stimulated emission in time sequence.
The analysis of the autoradiograph has been, heretofore, made by a person in such a manner that they have detected the distribution of the radioactively labeled substances on the support medium by visually observing an autoradiograph to obtain the locational information (and further informations such as the identification of the biopolymer, the molecular weight thereof and characteristics thereof based on the locational information) on the specific substances labeled radioactively. For instance, the base sequence of DNA is determined by measuring resolved portions (bands) of radioactively labeled base-specific DNA fragments or a mixture thereof with eyes and comparing the resolved portions among resolved rows of the DNA fragments with each other.
The term "visualized autoradiograph" used herein generally means a radiation image of radioactively labeled substances on a radiographic film, which is obtained by placing a support medium containing the labeled substances resolved (developed) and the radiographic film together in layers to expose the film. For instance, the visible image of autoradiograph is such an image as shown in FIG. 1 (practically, a photographic image having various shade in density is obtained on a film). FIG. 1 shows an example of an electrophoretic pattern in which radioactively labeled DNA fragments are resolved in four rows on a gel support medium through electrophoresis. In FIG. 1, each of black bands represents an electrophoresed portion of DNA fragments. In the above-mentioned radiation image recording and reproducing method, the same autoradiographic image can be obtained on a photographic film by reproducing it from electric signals which are obtained by reading out the stimulable phosphor sheet through an appropriate conversion means. Before the visualization of the autoradiograph, the electric signals can be subjected to various image processing to thereby facilitate the visual analysis of the autoradiographic image.
On the thus-obtained visible image of autoradiograph, however, there are mainly indicated two-dimensional locations of radioactively labeled substances as shown in FIG. 1, and it is almost impossible to accurately determine radiation intensity (namely, amounts of the radioactively labeled substances in proportion thereto) therefrom.
In order to facilitate the analysis of autoradiograph, there has been proposed a method in which electric signals corresponding to the autoradiograph are subjected to image processing such as gradation processing and then the autoradiograph is displayed as an image. However, an extra display device such as graphic display for gradation must be used and cost for analysis is expensive.
To reduce time and labor required for visual analysis and to improve the accuracy of analytical information, there have been previously proposed some methods for automatically obtaining locational information on the radioactively labeled substances in the form of symbols and/or numerals by converting the autoradiograph of the labeled substances distributed in at least one-dimensional direction on a support medium into digital signals and subjecting the digital signals to appropriate signal processing, as disclosed in Japanese Patent Provisional Publications No. 59(1984)-126527 and No. 59(1984)-126278 (which respectively correspond to U.S. application Ser. Nos. 568,877 (now U.S. Pat. No. 4,777,597) , and now U.S. Pat. No. 4,777,597 and application Ser. No. 568,875 which is pending), etc. Said digital signals corresponding to the autoradiograph can be obtained by visualizing the autoradiograph on a radiographic film according to the conventional radiography and photoelectrically reading out it by means of reflected light or transmitted light. Alternatively, when a stimulable phosphor sheet is used, said digital signals can be obtained by directly reading out the phosphor sheet on which the autoradiograph is stored and recorded.
Further, there have been proposed methods which comprise electrically displaying an image of original autoradiograph (resolved pattern) on CRT, inputting information required for analysis on the basis of the display image and subjecting digital signals corresponding to the autoradiograph to signal processing according to the input information, namely semi-automatic analytical methods of autoradiograph, as disclosed in Japanese Patent Applications No. 60(1985)-62298 and 60(1985)-62299 (which correspond to U.S. application Ser. No. 844,967 now U.S. Pat. No. 4,837,687).